In the art of adjustable threshold assemblies, for example, of the general type disclosed in U.S. Pat. No. 3,762,100 and No. 3,967,412, a vertically adjustable horizontal rail member extends below the bottom edge of the movable door and is supported by a wooden base member which also supports an extruded aluminum sill member. An extruded vinyl sealing element is retained by the sill member and engages the front surface of the adjustable rail member to form a seal with the rail member to avoid the accumulation of dirt and the flow of water and air into and through the cavity under the rail member. It is also known to construct the sill member in two sections and to connect the sections with a thermal barrier of plastics material, for example, as disclosed in U.S. Pat. No. 3,346,994.
As indicated above, it is highly desirable to prevent water from seeping into the cavity below the rail member and then through or around the threshold assembly into the sub-flooring or the adjacent floor covering, especially after vertical adjustment of the rail member. It is also desirable to obtain a dependable water-tight seal between opposite ends of the threshold assembly and the adjacent door jambs so that water does not flow around the ends of the sill and rail members and back into the cavity under the rail member and/or into the sub-flooring or floor covering.